A new study suggests that a million or more European Christians were enslaved by Muslims in North Africa between 1530 and 1780 – a far greater number than had ever been estimated before.

In a new book, Robert Davis, professor of history at Ohio State University, developed a unique methodology to calculate the number of white Christians who were enslaved along Africa’s Barbary Coast, arriving at much higher slave population estimates than any previous studies had found.

Most other accounts of slavery along the Barbary coast didn’t try to estimate the number of slaves, or only looked at the number of slaves in particular cities, Davis said. Most previously estimated slave counts have thus tended to be in the thousands, or at most in the tens of thousands. Davis, by contrast, has calculated that between 1 million and 1.25 million European Christians were captured and forced to work in North Africa from the 16th to 18th centuries.

“Much of what has been written gives the impression that there were not many slaves and minimizes the impact that slavery had on Europe,” Davis said. “Most accounts only look at slavery in one place, or only for a short period of time. But when you take a broader, longer view, the massive scope of this slavery and its powerful impact become clear.”

Davis said it is useful to compare this Mediterranean slavery to the Atlantic slave trade that brought black Africans to the Americas. Over the course of four centuries, the Atlantic slave trade was much larger – about 10 to 12 million black Africans were brought to the Americas. But from 1500 to 1650, when trans-Atlantic slaving was still in its infancy, more white Christian slaves were probably taken to Barbary than black African slaves to the Americas, according to Davis.

“One of the things that both the public and many scholars have tended to take as given is that slavery was always racial in nature – that only blacks have been slaves. But that is not true,” Davis said. “We cannot think of slavery as something that only white people did to black people.”

During the time period Davis studied, it was religion and ethnicity, as much as race, that determined who became slaves.

“Enslavement was a very real possibility for anyone who traveled in the Mediterranean, or who lived along the shores in places like Italy, France, Spain and Portugal, and even as far north as England and Iceland,” he said.

Pirates (called corsairs) from cities along the Barbary Coast in north Africa – cities such as Tunis and Algiers – would raid ships in the Mediterranean and Atlantic, as well as seaside villages to capture men, women and children. The impact of these attacks were devastating – France, England, and Spain each lost thousands of ships, and long stretches of the Spanish and Italian coasts were almost completely abandoned by their inhabitants. At its peak, the destruction and depopulation of some areas probably exceeded what European slavers would later inflict on the African interior.

Although hundreds of thousands of Christian slaves were taken from Mediterranean countries, Davis noted, the effects of Muslim slave raids was felt much further away: it appears, for example, that through most of the 17th century the English lost at least 400 sailors a year to the slavers.

Even Americans were not immune. For example, one American slave reported that 130 other American seamen had been enslaved by the Algerians in the Mediterranean and Atlantic just between 1785 and 1793.

Davis said the vast scope of slavery in North Africa has been ignored and minimized, in large part because it is on no one’s agenda to discuss what happened.

The enslavement of Europeans doesn’t fit the general theme of European world conquest and colonialism that is central to scholarship on the early modern era, he said. Many of the countries that were victims of slavery, such as France and Spain, would later conquer and colonize the areas of North Africa where their citizens were once held as slaves. Maybe because of this history, Western scholars have thought of the Europeans primarily as “evil colonialists” and not as the victims they sometimes were, Davis said.

Davis said another reason that Mediterranean slavery has been ignored or minimized has been that there have not been good estimates of the total number of people enslaved. People of the time – both Europeans and the Barbary Coast slave owners – did not keep detailed, trustworthy records of the number of slaves. In contrast, there are extensive records that document the number of Africans brought to the Americas as slaves.

So Davis developed a new methodology to come up with reasonable estimates of the number of slaves along the Barbary Coast. Davis found the best records available indicating how many slaves were at a particular location at a single time. He then estimated how many new slaves it would take to replace slaves as they died, escaped or were ransomed.

“The only way I could come up with hard numbers is to turn the whole problem upside down – figure out how many slaves they would have to capture to maintain a certain level,” he said. “It is not the best way to make population estimates, but it is the only way with the limited records available.”

Putting together such sources of attrition as deaths, escapes, ransomings, and conversions, Davis calculated that about one-fourth of slaves had to be replaced each year to keep the slave population stable, as it apparently was between 1580 and 1680. That meant about 8,500 new slaves had to be captured each year. Overall, this suggests nearly a million slaves would have been taken captive during this period. Using the same methodology, Davis has estimated as many as 475,000 additional slaves were taken in the previous and following centuries.

The result is that between 1530 and 1780 there were almost certainly 1 million and quite possibly as many as 1.25 million white, European Christians enslaved by the Muslims of the Barbary Coast.

Davis said his research into the treatment of these slaves suggests that, for most of them, their lives were every bit as difficult as that of slaves in America.

“As far as daily living conditions, the Mediterranean slaves certainly didn’t have it better,” he said.

While African slaves did grueling labor on sugar and cotton plantations in the Americas, European Christian slaves were often worked just as hard and as lethally – in quarries, in heavy construction, and above all rowing the corsair galleys themselves.

Davis said his findings suggest that this invisible slavery of European Christians deserves more attention from scholars.

“We have lost the sense of how large enslavement could loom for those who lived around the Mediterranean and the threat they were under,” he said. “Slaves were still slaves, whether they are black or white, and whether they suffered in America or North Africa.”